The Plantar Support of the Navicular-Cunieform Joint

Abstract

Category: Midfoot/Forefoot Introduction/Purpose: Weight-bearing radiographic analysis of pes planus deformities shows, with varying degree of severity, a break in Meary’s line, uncovering of the talar head and an increase in talar-first metatarsal angle. Work by Alsousou (BOFAS 2016) has shown the break in Meary’s line to occur not only at the talonavicular joint (2/3rds of cases) but also at the navicular-cuneiform joint (1/3 rd of cases), distal to the spring ligament and reported posterior tibial tendon insertion. There are currently no anatomical studies analysing the medial longitudinal arch distal to the spring ligament insertion. We aimed to examine this area and assess the anatomy supporting the distal medial longitudinal arch. Methods: We examined 11 cadaveric lower limbs that had been preserved for dissection at the Human Anatomy and Resource Centre at Liverpool University, in a solution of formaldehyde. The lower limbs were carefully dissected to identify the plantar aspect of the medial longitudinal arch Results: In all specimens, the posterior tibial tendon inserted into the plantar medial aspect of the navicular with separate slips to the intermediate and lateral cuneiform. Following insertion, on the navicular, a tendon-like structure extended from this navicular insertion point to the medial cuneiform. This tendon-like structure is statically inserted between the navicular and medial cuneiform allowing the pull of tibialis posterior to act on the navicular and medial cuneiform in tandem. The average width of this ligament (15.2 mm) is much greater than that of the tibialis posterior tendon (9.5 mm). A separate smaller plantar ligament is also present between the navicular and medial cuneiform. Conclusion: The posterior tibialis tendon inserts into the navicular, and what is likely an anthropological remnant, extends onto the medial cuneiform as the navicular cuneiform ligament. This provides a static restraint between two bony insertions and increases the lever arm of the posterior tibial tendon. The major support of the distal aspect of the medial longitudinal arch (i.e. the navicular-cuneiform joint) is provided by the substantial navicular cuneiform ligament.